If you pull big chunks of the foam, it probably fractured parts you can't see. You should be able to patch it and seal the seams with KerdiFix, or if using Wedi, their proprietary adhesive, but it's...

The 'sand' in an epoxy grout is more for visual effects than strength, so it's not super critical about being exact unless you need to mix more than one batch so that they can match. The 'sand' is a...